It would, in my opinion, have to ignore Ruby's protestations about "not being like the other demons". But then I have always felt that Ruby before Dean's trip to hell, was trying to help them, but what they did to her (Leaving her in the Devil's trap to be found by Lilith) most likely made her change camps. (and who can blame here. Imagine the kind of torture she had to go through for trying to help the brothers.) But Sam would not have that insight, per-say, so his subconscious seeing his drinking of Ruby's blood as a betrayal of Dean, means he has suspicious about Ruby.

Or it might be his psychic abilities kicking in and trying to warn him of the true dangers that Ruby presents. (I'm leaning towards this as the answer.)

PS: Not via-ing for the cameo...not yet...just giving one of my standard reviews. LOL